We propose to use the nematode Caenorhabditis elegans to test the hypothesis that reduced metabolism causes extended life span and to test whether oxidative stress is the most likely biochemical mechanism. We have developed a sensitive method for measuring the metabolic rate in small populations of C. elegans by their production of CO2. We have used this to show that several long-lived mutants all have reduced metabolic rates relative to wild-type strains, and that a genetic suppressor of one of these mutants that restores life span to normal also restores metabolic rate to normal. In addition, worm life span is increased at lower temperatures which also reduce metabolic rates. These findings suggest that reduced metabolic rate could cause the increased life span in these mutants. One likely biochemical mechanism to explain these correlations is that reduced metabolism reduces oxidative stress from reactive oxygen species that are inevitable byproducts of oxidative metabolism. We will pursue the following specific aims: (1) Determine if additional long-lived C. elegans strains have reduced metabolic rate like those already tested. We will determine the metabolic rate of several alleles of all of the long-lived mutants which have been identified and of several wild isolates and other strains. We expect many of these will show reduced metabolic rate, but if strains are found with extended life span and normal metabolism, these may have mutants in genes controlling antioxidants or repair systems, and these will be characterized further. (2) Determine whether reduced metabolic rate corresponds with increasing life span in other ectothermic animals by measuring the metabolic rate of Drosophila strains with extended life span. This will be done in collaboration with Dr. Jim Curtsinger from the University of Minnesota. (3) Determine if altering the oxygen level during growth alters life span as predicted by the oxidative stress theory of aging. This will be done by varying oxygen levels to vary oxidative stress and measuring biochemical markers for oxidative damage to see if increased damage correlates with reduced longevity. (4) Identify additional genes that can mutate to increase life span without reducing metabolism. These would be candidates for protecting from oxidative stress. The significance of this work is its direct application to the causes of human aging. We will test one of the most widely held theories of aging and identify new genes whose products play a role in determining longevity and learn more about the function of known genes. These will offer new targets for drugs and other therapeutic approaches to slow down the aging process and improve health span.